Author Topic: Theoretical FTL  (Read 47239 times)

gospacex

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Re: Theoretical FTL
« Reply #40 on: 08/05/2008 08:22 AM »
any sufficiently dense object (possibly a neutron star just a bit shy of unrestrained collapse) can have a photon sphere. That is, the object through it's deep gravity well can actually trap photons in orbit around the object. Anything moving slower than that will be trapped in higher orbits. One can then attempt to scatter observable stuff off of what is in the photon sphere.

I don't think so. Photon sphere is not a stable orbit, you can't "accumulate" orbiting photons there. IIRC lowest stable orbit around non-rotating black hole has a radius of 3*Rs.

I'm not sure I understand what you're saying. This would be an orbit, then you effectively have that photon trapped in this zone. It can still escape either by hitting other things or due to the quantum nature of the photon, tunneling either into the massive object or out of the system.

Stable orbit is an orbit where small perturbations result in small changes of orbit.

The "photon sphere" is not such an orbit, neither any other orbit closer than three Schwarzschild radii. Even though theoretically an object (or photon) with *exactly* the right kinetic energy and direction of flight can be put on these orbit, even tiniest error in speed or direction will change this orbit into a spiral trajectory either falling into the hole or going outward until the object is on orbit >= 3 Rs.

The closest such unstable orbit is at 3/2 Rs and it requires "objects" to have v=c. In other words, only photons can be put on this orbit. But "can be put" is not equal to "there are lots and lots of photons on this orbit". Actually, most of the time (read: always) this orbit is empty.
« Last Edit: 08/05/2008 08:23 AM by gospacex »

sandrot

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Re: Theoretical FTL
« Reply #41 on: 08/13/2008 10:02 PM »
"Paper planes do fly much better than paper spacecrafts."

colbourne

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Re: Theoretical FTL
« Reply #42 on: 12/04/2011 11:32 AM »
Have we discovered any more about the properties of anti-matter to answer the ideas raised in this thread yet ?

I think it is fair to say that we have more doubt now on the definite limits imposed by Einsteins theories and scientists are willing to speculate on the possibility of FTL.

This thread is also relevant :-

http://forum.nasaspaceflight.com/index.php?topic=24858.0

JohnFornaro

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Re: Theoretical FTL
« Reply #43 on: 12/04/2011 02:55 PM »
Why don't we prove the characteristics of anti-matter first?  It takes very little thought, and not that much more typing to come up with usefull applications for anti-gravity.
Sometimes I just flat out don't get it.

Joris

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Re: Theoretical FTL
« Reply #44 on: 12/04/2011 08:19 PM »
Assumption 1
===========
I am assuming that anti-matter wil be affected by gravity in the reverse to normal matter.

Assumption 2
===========
Therefore if we can create an anti matter object we should be able to accelerate it up to FTL. This in itself should allow FTL communications.

Assumption 3
===========

We can currently contain anti-matter by magnetic means, so we should be able to contain normal matter by a similar means inside our anti-matter spacecraft.

I expect the new CERN accelrator will be able to answer my probably incorrect assumptions.

Nope, basic knowledge will do.

First two are wrong.
Third is irrelevant.
JIMO would have been the first proper spaceship.

colbourne

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Re: Theoretical FTL
« Reply #45 on: 12/04/2011 08:29 PM »
Assumption 1
===========
I am assuming that anti-matter wil be affected by gravity in the reverse to normal matter.

Assumption 2
===========
Therefore if we can create an anti matter object we should be able to accelerate it up to FTL. This in itself should allow FTL communications.

Assumption 3
===========

We can currently contain anti-matter by magnetic means, so we should be able to contain normal matter by a similar means inside our anti-matter spacecraft.

I expect the new CERN accelrator will be able to answer my probably incorrect assumptions.

Nope, basic knowledge will do.

First two are wrong.
Third is irrelevant.

How did you know that the first two were wrong ?

Joris

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Re: Theoretical FTL
« Reply #46 on: 12/04/2011 08:37 PM »
How did you know that the first two were wrong ?

Observed since the moment we discovered anti-particles.

An example:
An electron and a positron are antiparticles of each other.
They exhibit perfectly predictable behavior.

How big is your understanding of physics, it is good to know before continouing this discussion?
JIMO would have been the first proper spaceship.

colbourne

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Re: Theoretical FTL
« Reply #47 on: 12/05/2011 01:15 PM »
How did you know that the first two were wrong ?

Observed since the moment we discovered anti-particles.

An example:
An electron and a positron are antiparticles of each other.
They exhibit perfectly predictable behavior.

How big is your understanding of physics, it is good to know before continouing this discussion?

I think you better let CERN and other research establishments know, as they are spending a fortune to confirm the properties of anti-matter. As far as I know the exact properties have not been confirmed yet.

I only have a BSc in Physics

Tass

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Re: Theoretical FTL
« Reply #48 on: 12/05/2011 01:35 PM »
I think you better let CERN and other research establishments know, as they are spending a fortune to confirm the properties of anti-matter. As far as I know the exact properties have not been confirmed yet.

I only have a BSc in Physics

Oh sure they do, but it is more to check much more subtle things that wether their mass is negative.

We know antimatters charge is reversed (positronium is bound for example), we thus know from electromagnetic effects on antimatter that its inertial mass is positive. We don't strictly know that the gravitational mass is positive, no one has meassured the gravitational mass of antimatter (it is very hard to do), but having positive energy and negative gravitational mass would be very hard to reconcile with general relativity.

KelvinZero

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Re: Theoretical FTL
« Reply #49 on: 12/05/2011 06:07 PM »
Here is a wiki link. Very strongly expected to have the usual gravity though not yet experimentally confirmed.
http://en.m.wikipedia.org/wiki/Gravitational_interaction_of_antimatter

Joris

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Re: Theoretical FTL
« Reply #50 on: 12/05/2011 08:15 PM »
Okay fine let us assume anti-matter induces anti-gravity.
This raises a few questions:

A photon is its own antiparticle, how does it act under gravity?

How will particle-antiparticle parirs act under gravity? (charmonium, for example.)

Will an object that has a left side made of antimatter accelarate to the right?

The first one is observed, albeit raises questions about whether gravity is a two component force. (Mass-gravity and energy-gravity.)

The second two are thought-experiments, untill tested, but make me doubt it.

(IMHO, I think that it is best to assume that antimatter acts as predictable as matter with respect to the Standardmodel. At least untill we have an explanation for gravity.)

On a side note: I'm interested what direction you went after getting your BSc in physics: business, research, education, something else?
JIMO would have been the first proper spaceship.

Cherokee43v6

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Re: Theoretical FTL
« Reply #51 on: 12/05/2011 08:37 PM »
Even this business major knows that gravity is considered to be a function of mass, not of charge.

There is no such thing (so far) as 'antimass'.
"I didn't open the can of worms...
...I just pointed at it and laughed a little too loudly."

colbourne

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Re: Theoretical FTL
« Reply #52 on: 12/05/2011 09:18 PM »
I am just saying that we have no knowledge of how gravity affects anti-matter and there is thus a possibility that it will act differently to normal matter with gravity. If so it might explain the discrepancy between the amount of matter versus anti-matter in the observed universe (It has simply accelerated away from us and could explain the accelerating expansion of the universe, removing the requirement for dark matter).

I designed visual systems for Singer flight simulators after getting my BSc.

Tass

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Re: Theoretical FTL
« Reply #53 on: 12/06/2011 08:18 AM »
Even this business major knows that gravity is considered to be a function of mass, not of charge.

That is hardly relevant. Antiparticles are not just charge reversed. They are apparently everything-but-mass reversed. Some people speculate that they may be mass reversed as well. You are right there is probably no anti-mass. It is very unlikely, but the premise of this thread is "what if".

KelvinZero

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Re: Theoretical FTL
« Reply #54 on: 12/06/2011 08:37 AM »
Even this business major knows that gravity is considered to be a function of mass, not of charge.

That is hardly relevant. Antiparticles are not just charge reversed. They are apparently everything-but-mass reversed. Some people speculate that they may be mass reversed as well. You are right there is probably no anti-mass. It is very unlikely, but the premise of this thread is "what if".

Also many physicists are dedicating themselves to somehow unifying the concepts of gravity and charge. Im probably misusing the terms a bit but that is essentially what the search for the Grand Unified Theory is all about.
http://en.wikipedia.org/wiki/Grand_Unified_Theory

JohnFornaro

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Re: Theoretical FTL
« Reply #55 on: 12/06/2011 12:53 PM »
Quote from: Colbourne
I think you better let CERN and other research establishments know, as they are spending a fortune to confirm the properties of anti-matter. As far as I know the exact properties have not been confirmed yet.

It is true that all the properties of anti-m have not yet been discovered.  It is your first assumption, made without specific knowledge of the properties, that anti-m would also have anti-g properties.  Since some properties of anti-m are known, it is currently accepted that there is no such thing.  Like Kelvin said; "Very strongly expected to have the usual gravity though not yet experimentally confirmed".

But since, as Tass observes, "the premise of this thread is 'what if'", then one is free, more or less, to talk up the fantastic possibilities of FTL.  It is very easy to do.  Is that all you wish to do?
Sometimes I just flat out don't get it.

Tass

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Re: Theoretical FTL
« Reply #56 on: 12/06/2011 03:46 PM »
I will just note that anti-gravity would still not enable faster-than-light.

Negative gravitational and inertial mass would, however, allow you to accelerate without bound.

scienceguy

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Re: Theoretical FTL
« Reply #57 on: 12/06/2011 05:33 PM »
Wouldn't negative mass be both antigravity and negative inertia? I'm thinking of papers by Bondi (1957) and Forward (1990).

Bondi, H. (1957) Negative mass in general relativity. Reviews of Modern Physics 29(3):423-428

Forward, R. L. (1990) Negative matter propulsion. Journal of Propulsion and Power 6(1):28-37
e^(pi*i) = -1

scienceguy

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Re: Theoretical FTL
« Reply #58 on: 12/06/2011 05:46 PM »
Oops! I realize the authors in those papers distinguish between negative inertial mass and negative gravitational mass.
e^(pi*i) = -1

RanulfC

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Re: Theoretical FTL
« Reply #59 on: 12/06/2011 06:07 PM »
I recall a lot of "speculative-fiction" about anti-matter when it was first discovered/postulated, much of it dealing with the concepts and ideas of what-and-how "contra-terrene" (Cee-Tee was the "popular" name at the time) matter would "interact" with the "standard" universe.

Nothing in the theoretical or observered work indicates "anti-gravity" properties and other than the "mutual-anihilation" aspect antimatter was supposed to simply be a "negativily" charged analog to normal matter. However one rather "glaring" early assumption seems to be "missing" from observed anti-matter phenomon; we don't find mucn (if any) actual "anti-matter" in the universe around us.

The theory (and assumptions) have always been that IF antimatter exists in nature then it SHOULD behave similarly to normal matter in that it SHOULD aggrate together into particles, molecules, and solid representations of "anti-matter"... So the question is where IS the "anti-asteroids," "anti-planets," and "anti-suns" one would expect to find? (Of course one then needs to delve into the exact details of "how" you'd tell the difference barring the catastrophic method of verification

Now I'm pretty much expecting my memory is wrong but I seem to recall that a question that has been raised during work on the various things like the "Mach-Effect" and other "alternative" theories on the nature of the universe that struck me was; "We have always pretty much "assumed" that Mass generates gravity, the more mass the higher the gravity. An interesting question though is this: What if mass does NOT 'generate' gravity as we understand it but it is simply that normal matter "concentrates" gravity?"

This leads to the thought that the lack of observed mass' of "anti-iron" etc, might be because anti-matter since it isn't "normal" matter might actually have the opposite effect? Note that this is NOT "anti-gravity" though it's possible it could produce a somewhat similar effect given enough of it, the problem would be since normal matter SEEMS to acumulate due to an increasing mass/increasing gravity in-falling effect, anti-matter would NOT act the same and in fact would be almost impossible for it to accumulate in the "normal" manner.

Thoughts?
(Ok, OTHER than the ones about me being "Crazy" and a "Freak-a-zoid-Nut-Case" Lets concentrate on the "concept" and not my already diagnosed mental issues )

Randy
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British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

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